Green’s Dictionary of Slang

a promiscuous woman.

1894		People 4 Feb. in Ware (1909) 17/2: Witnesses took several names and addresses, and some of the females described themselves as ‘Banburys’, and said they got their living as best they could.
1909		J. Ware Passing Eng. of the Victorian Era 17/2: Banbury (London, 1894). One of the more recent shapes of ‘jam’, ‘biscuit’, ‘cake’, ‘confectionery’, ‘tart’ — a loose woman.
2003		Indep. Rev. 1 Oct. 5: She has a reputation as a bit of a Banbury Cross equestrian.